package com.parkwalk.xxx.ui.security;

import java.util.zip.Checksum;

public class CRC16_CCITT implements Checksum {
    private static final int[] CRC_TABLE = {0, 4129, 8258, 12387, 16516,
            20645, 24774, 28903, 33032, 37161, 41290, 45419, 49548, 53677,
            57806, 61935, 4657, 528, 12915, 8786, 21173, 17044, 29431, 25302,
            37689, 33560, 45947, 41818, 54205, 50076, 62463, 58334, 9314,
            13379, 1056, 5121, 25830, 29895, 17572, 21637, 42346, 46411, 34088,
            38153, 58862, 62927, 50604, 54669, 13907, 9842, 5649, 1584, 30423,
            26358, 22165, 18100, 46939, 42874, 38681, 34616, 63455, 59390,
            55197, 51132, 18628, 22757, 26758, 30887, 2112, 6241, 10242, 14371,
            51660, 55789, 59790, 63919, 35144, 39273, 43274, 47403, 23285,
            19156, 31415, 27286, 6769, 2640, 14899, 10770, 56317, 52188, 64447,
            60318, 39801, 35672, 47931, 43802, 27814, 31879, 19684, 23749,
            11298, 15363, 3168, 7233, 60846, 64911, 52716, 56781, 44330, 48395,
            36200, 40265, 32407, 28342, 24277, 20212, 15891, 11826, 7761, 3696,
            65439, 61374, 57309, 53244, 48923, 44858, 40793, 36728, 37256,
            33193, 45514, 41451, 53516, 49453, 61774, 57711, 4224, 161, 12482,
            8419, 20484, 16421, 28742, 24679, 33721, 37784, 41979, 46042,
            49981, 54044, 58239, 62302, 689, 4752, 8947, 13010, 16949, 21012,
            25207, 29270, 46570, 42443, 38312, 34185, 62830, 58703, 54572,
            50445, 13538, 9411, 5280, 1153, 29798, 25671, 21540, 17413, 42971,
            47098, 34713, 38840, 59231, 63358, 50973, 55100, 9939, 14066, 1681,
            5808, 26199, 30326, 17941, 22068, 55628, 51565, 63758, 59695,
            39368, 35305, 47498, 43435, 22596, 18533, 30726, 26663, 6336, 2273,
            14466, 10403, 52093, 56156, 60223, 64286, 35833, 39896, 43963,
            48026, 19061, 23124, 27191, 31254, 2801, 6864, 10931, 14994, 64814,
            60687, 56684, 52557, 48554, 44427, 40424, 36297, 31782, 27655,
            23652, 19525, 15522, 11395, 7392, 3265, 61215, 65342, 53085, 57212,
            44955, 49082, 36825, 40952, 28183, 32310, 20053, 24180, 11923,
            16050, 3793, 7920};

    private int crc = 65535;

    public long getValue() {
        return this.crc & 0xFFFFFFFF;
    }

    public void reset() {
        this.crc = 0;
    }

    public void update(byte[] b) {
        this.crc = updateBytes(this.crc, b, 0, b.length);
    }

    public void update(byte[] b, int off, int len) {
        if (b == null) {
            throw new NullPointerException();
        }
        if ((off < 0) || (len < 0) || (off > b.length - len)) {
            throw new ArrayIndexOutOfBoundsException();
        }

        this.crc = updateBytes(this.crc, b, off, len);
    }

    public void update(int b) {
        this.crc = update(this.crc, b);
    }

    private int update(int crc, int b) {
        crc = (crc & 0xFF) << 8
                ^ CRC_TABLE[(((crc & 0xFF00) >>> 8 ^ b) & 0xFF)];
        return crc;
    }

    private int updateBytes(int crc, byte[] b, int off, int len) {
        for (int i = off; i < off + len; i++) {
            crc = update(crc, b[i]);
        }

        return crc;
    }
}